Method for manufacture of elastomeric alloys using recycled rubbers

ABSTRACT

Disclosed is a method of preparing a thermoplastic resin composition that includes combining a ground crosslinked rubber with a thermoplastic resin and a compatibilizer based on a paraffinic oil to form a blend thermoplastic composition. The ground crosslinked rubber has an average particle size of about 80 mesh or smaller. The thermoplastic resin includes at least one polyolefinic resin. The ground crosslinked rubber is included in amounts of up to about 70% by weight, based on the weight of the blend thermoplastic composition.

FIELD OF THE INVENTION

The present invention is directed to a method of preparing blendthermoplastic compositions using particles of recycled vulcanized, orcrosslinked, rubber and to the compositions made by the method andarticles formed from these compositions. The thermoplastic compositionsproduced by the method may be formed into many products, includingautomotive and industrial components.

BACKGROUND AND SUMMARY OF THE INVENTION

Both manufacturers and the general public have placed an emphasis inrecent years on recycling materials. Recycling materials is desirablefrom the standpoint of reducing waste that must be landfilled, burned,or otherwise discarded. It has become desirable for manufacturers toinclude recycled plastic or recycled rubber content in the manufactureof articles. In some instances, recycled materials may also offer a costadvantage over virgin materials.

Recycling of thermoset polymeric materials, however, has faced seriousdifficulties in the preparation of materials for recycling and inmaintaining desired properties for the articles that incorporaterecycled material. One avenue for recycling crosslinked rubbers has beenthe use of ground crosslinked rubber as a filler in new thermosetpolymeric materials. Ground crosslinked rubber may be produced in meshsizes of from 10 to over 300, with a typical range being about 40-80mesh. The ground crosslinked rubber has commonly been recycled by addingit to uncrosslinked rubber and then vulcanizing the blend rubber. Ingeneral, it has been reported in literature that blends cannot includemore than about 10% recycled rubber without suffering a significantdecrease in properties, including surface roughness. Mixtures includingup to 30% ground crosslinked rubber in new rubber have been reported tohave somewhat lower tensile strength as compared to virgin rubber.

One solution to the problem of how to incorporate larger amounts ofrecycled rubber without a decrease in properties is to chemically treatthe recycled rubber. Stosky reported in "Innovation in the Developmentand Use of Recycled Rubber," Paper No. 42, Rubber Division, AmericanChemical Society (May 6-9, 1997) that chemically treated recycled rubbercould be incorporated in amounts of up to 75% in a blend with virginrubber, resulting in a material having equivalent or even superiorperformance as compared to virgin rubber. The chemical treatment appearsto involve a surface treatment that allows for crosslinks between theground crosslinked rubber and the virgin thermosetting material. Anothermethod of recycling rubber involves de-vulcanizing the rubber byphysical or chemical means. De-vulcanized rubber may be mixed withvirgin material, re-molded, and then re-vulcanized along with the newmaterial to produced a crosslinked blend. A process of treating groundcrosslinked rubber with a caustic gas to allow bonding with otherpolymers has also been reported.

These methods, however, involve added reactions and manufacturing stepsthat make recycling of materials more expensive. Moreover, these methodsare directed to thermoset materials only. Thus, the need remains for arelatively simple and effective means of recycling cured rubber scrapinto new articles, particularly articles formed from thermoplasticcompositions.

The present invention provides a method of recycling a cured EPDMterpolymer or EPR copolymer rubber, or mixtures including these rubbers,by blending the recycle rubber into a thermoplastic polyolefin resin toform a blend composition. The blend compositions comprise groundcrosslinked rubber having a particle size of about 80 mesh or smaller,preferably of about 120 mesh or smaller. (The mesh size is inverselyproportional to the particle size.) The compositions prepared accordingto the methods of the invention may include a surprisingly high level ofrecycle rubber without adverse effect on physical or aestheticproperties. Thus, the blend thermoplastic materials produced maycomprise up to about 70% by weight of the ground crosslinked rubber,based upon the total weight of the blend material. The thermoplasticblend materials of the invention also comprise at least onethermoplastic polyolefin resin and a compatibilizer.

DETAILED DESCRIPTION

The term "ground crosslinked rubber" as used in relation to the methodsand compositions of the invention refers to at least partiallycrosslinked or vulcanized rubber that has been reduced to particles.Preferably, the rubber is fully crosslinked; i.e., the crosslinking hasbeen carried to an extent that formation of further crosslinks, ifpossible, would not substantially improve the physical properties of therubber. The particle size of the recycle ground crosslinked rubber ofthe invention is about 80 mesh or smaller, preferably about 120 mesh orsmaller, and it is especially preferred that the particle size be about200 mesh or smaller.

The ground crosslinked rubber particles may be prepared by a number ofmethods. In one method, the rubber is swelled with solvent and thenground to a fine particle size. The rubber may be ground cryogenically.In a preferred procedure, the recycled rubber particles are preparedaccording to the procedure in Rouse, U.S. Pat. No. 5,411,215,incorporated herein by reference. In this procedure, the rubber isground as a 10% by weight slurry in water of 10 mesh particles in aseries of grinding mills having progressively finer grinding stone.

The rubbers that may be recycled in the methods and compositions of theinvention are ethylene propylene rubber (also known as EPM or EPR),ethylene propylene diene monomer rubber (EPDM), and mixtures and blendsof these. The rubbers will be collectively referred to herein as EPDM.Mixtures and blends of EPDM with other rubbers may also be used, as wellas elastomeric alloys that include these rubbers. The rubber compound,which includes the rubber and any additives, may also typically includeup to about 50% additives, preferably up to about 15% additives, basedupon the weight of the rubber compound. Example of useful additivesinclude, without limitation, accelerators, oils, colorants and fillers,especially carbon black.

The ground crosslinked rubber is mixed with a thermoplastic component.The thermoplastic component is preferably a polyolefinic material. Amongpreferred materials are homopolymers of ethylene, propylene, andbutylene, and copolymers that include one or more of these monomers. Ina particularly preferred embodiment, the recycled ground crosslinkedrubber is ethylene propylene diene monomer rubber and the thermoplasticcomponent is selected from polyethylene, polypropylene, ethylenecopolymers, propylene copolymers, poly(ethylene propylene) copolymers,and combinations of these. In a particularly preferred embodiment, therubber particles comprise EPDM rubber that is at least partially cured,preferably fully cured, and the thermoplastic composition comprisespolypropylene.

The ground crosslinked rubber particles can be included in thethermoplastic composition in amounts of up to about 70% by weight, andpreferably up to about 60% by weight, based upon the total weight of theblend thermoplastic composition. Preferably, at least about 5% by weightof the recycle ground crosslinked rubber is included. The amount ofground rubber that is included is determined based upon the particularapplication and can readily be determined by straightforward testing.

The compositions of the invention also include a compatibilizer. Ingeneral, useful compatibilizers are plasticizers and oils that are usedto improve physical properties of the blend. It is particularlypreferred to include as a compatibilizer a paraffinic oil or derivativeof a paraffinic oil. A compatibilizer is included in amounts of at leastabout 1% by weight of the blend. It is preferred to include at leastabout 10% by weight compatibilizer, based upon the total weight of theblend thermoplastic material. Preferably, no more than about 25% byweight of compatibilizer is included in the compositions of theinvention.

Customary additives such as lubricants, fillers, pigments, plasticizers,surface-modifying additives, UV absorbers, antioxidants, hindered amineor amide light stabilizers, and so on may be added to the thermoplasticcomposition along with the ground crosslinked rubber and compatibilizer.Blends, particularly blends containing EPDM rubber that has not beenpigmented, can be colored to a desired color. For instance, anautomotive component formed from the blend may be colored to complementthe color of a vehicle body to which it is to be attached.

In general, there must be enough of the thermoplastic material to holdthe alloy together. There should also be adequate dispersion ordistribution of the rubber particles in the thermoplastic resin medium.When the blend thermoplastic material is used in an injection moldingoperation, the blend thermoplastic material may include up to about 70%by weight, preferably up to about 60%, of the rubber particles. Whenlower compression set (as may be measured by ASTM 395) is needed, theamount of rubber is higher; however, lower levels of rubber are includedwhen surface properties, such as surface smoothness, are important. Whenthe blend thermoplastic material is to be extruded, a lower weightpercentage of rubber particles, such as less than about 40% by weight,may be used to obtain better surface smoothness.

The invention embraces a broad range with respect to levels of therubber particles that may be included in the blend compositions, and theparticular percentage by weight of rubber particles may be chosen tosuit the article to be manufactured from the blend. In general, thecompression set improves, or decreases, with higher levels of the rubberparticles. Tensile properties, however, are generally better with lowerlevels of rubber particles in the blend thermoplastic material. Thus, itis necessary to balance the levels of the thermoplastic and the rubberparticles in the thermoplastic material in view of the propertiesrequired for the ultimate article that is to be made from it. The blendthermoplastic materials of the invention typically have hardnesses ofabout 60 Shore A, and hardnesses of up to about 60 Shore D are possible.When the rubber particles are included in higher amounts, it ispreferred that the molding or shaping conditions be controlled so thatthe surface of the part being formed is the thermoplastic component ofthe blend.

The blend thermoplastic material of the invention is particularly usefulas a replacement for conventional rubber materials. The blendthermoplastic material offers several advantages over materials that arepresently available. First, the materials are less expensive due to theutilization of recycled rubber. Secondly, the blend thermoplasticmaterials, like other thermoplastic compositions, may be remelted andreformed. In addition, the process by which the blend thermoplasticmaterials of the invention is manufactured is more straightforward andless sensitive to manufacturing conditions as compared to manufacture ofrubbers containing recycled rubber. Moreover, the present blendthermoplastic material may be prepared using the equipment usuallyemployed in preparing thermoplastic blends rather than the specializedequipment required for dynamic vulcanization.

The blend thermoplastic materials of the invention may be prepared bymixing the thermoplastic composition, additives, includingcompatibilizer, and the rubber particles in either a continuous or batchprocess. Such processes may be carried out using, for example andwithout limitation, twin screw extruders, Buss extruders, continuousmilling lines, or with a high-shear or low-shear mixer. The mixture maythen be extruded and pelletized according to usual methods. The pelletsmay be either packaged for future use or used immediately in a processof forming an article. The pellets or blends of the invention may beformed into articles according to any of the methods known in the artfor thermal processing of thermoplastic resin compositions. For example,compression molding, vacuum molding, injection molding, thermoforming,blow molding, calendering, casting, extrusion, filament winding,laminating, rotational or slush molding, transfer molding, lay-up orcontact molding, stamping, and combinations of these methods may be usedwith the blend thermoplastic materials.

The blend thermoplastic materials of the invention may be formed intomany different kinds of articles. In particular, the blend thermoplasticmaterials of the invention may be formed into seals, seal extensions,and other automotive components. Articles that need low compression setare particularly suited for the blend materials of the invention.

The invention is further described and illustrated by the followingexamples. The examples are intended to be instructive and do not in anyway limit the scope of the invention as described and claimed.

EXAMPLES Example 1

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Recycle ground EPDM, 200 mesh                                                                        100                                                    W110 polypropylene (available from Rexene                                                              60                                                   Products Co., Dallas, TX)                                                     Flexon 885 Paraffinic Oil (available from Exxon                                                       30                                                    Chemical Co., Houston, TX)                                                    Silica FK500LS (available from Degussa Corp.,                                                          3                                                    Ridgefield Park, NJ)                                                          Antioxidant                                                        0.2        Lubricant                                                                     ______________________________________                                                               0.4                                                

Example 2

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Recycle ground EPDM, 120 mesh                                                                        100                                                    3T1A polypropylene (available from Rexene                                                              234                                                  Products Co., Dallas, TX)                                                     Flexon 885 Paraffinic Oil (available from Exxon                                                       50                                                    Chemical Co., Houston, TX)                                                    Silica FK500LS (available from Degussa Corp.,                                                          3                                                    Ridgefield Park, NJ)                                                          Antioxidant                                                        0.2        Lubricant                                                                     ______________________________________                                                               0.4                                                

Example 3

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Recycle ground EPDM, 120 mesh                                                                        100                                                    W110 polypropylene (available from Rexene                                                              67                                                   Products Co., Dallas, TX)                                                     Flexon 885 Paraffinic Oil (available from Exxon                                                       25                                                    Chemical Co., Houston, TX)                                                    Silica FK500LS (available from Degussa Corp.,                                                          3                                                    Ridgefield Park, NJ)                                                          Antioxidant                                                        0.2        Lubricant                                                                     ______________________________________                                                               0.4                                                

The ingredient of the examples were mixed in a low shear mixer, thenextruded and pelletized. Plaques of 6'×6' were injection molded from thecompositions of Examples 1-3 and from several commercially availablematerials. The plaques were tested to compare the properties of thecompositions of the invention to the properties of the commerciallyavailable materials. (The SANTOPRENE materials are available fromAdvanced Elastomer Systems, Akron, Ohio; the MULTIBASE material isavailable from Multibase Co., Inc. Copley, Ohio.) The results of thetesting are set out in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                            Santoprene                                                                          Santoprene                                                                          Multibase                                 Property       Example 2                                                                          Example 3                                                                         121-65W233                                                                             79W233                                                                                MFA 6406                                                                       Rubber                              __________________________________________________________________________    Hardness 72   45   35   72    79    65    65                                  (ASTM D2240)                                                                                   Shore D                                                                            Shore D                                                                            Shore A                                                                                Shore A                                                                            Shore A                                                                           Shore A                          Compression Set,                                                                                                              25 max.                       22 hr. @ 70 C (%)                                                             (ASTM D395)                                                                   Tensile at Break                                                                            803                                                                                     1235                                                                                                  1160                          (psi)                                                                         (ASTM D412)                                                                   Elongation at                                                                                                                 150                           Break (%)                                                                     (ASTM D412)                                                                   *Fogging, 3 hr. @                                                                          98                                                                                                               70 min.                       100 C (%)                                                                                           (pass)                                                                               (fail)                                                                                     (fail)                              (Ford FLTM BO                                                                 116-03)                                                                       Tear Strength                                                                                         32           21        (1305 psi)                     (kN/m)                                                                        (ASTM D624)                                                                   __________________________________________________________________________     *Fogging must be ≧ 70 to be automotive quality.                   

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention.

What is claimed is:
 1. A method of preparing a rubber-blendthermoplastic composition, comprising the steps of:(a) providing aground crosslinked rubber having an average particle size of about 80mesh or smaller; and (b) combining the ground crosslinked rubber with athermoplastic polyolefinic material and a compatibilizer based on aparaffinic oil to form a blend thermoplastic resin composition.
 2. Amethod according to claim 1, wherein the blend thermoplastic compositioncomprises no more than about 70% by weight of the ground crosslinkedrubber.
 3. A method according to claim 1, wherein the rubber has anaverage particle size of about 120 mesh or smaller.
 4. A methodaccording to claim 1, wherein the rubber has an average particle size ofabout 200 mesh or smaller.
 5. A method according to claim 1, wherein thethermoplastic polyolefinic material comprises a member selected from thegroup consisting of: homopolymers and copolymers of ethylene, propylene,and butylene, and combinations thereof.
 6. A method according to claim1, wherein the thermoplastic polyolefinic material comprises a memberselected from the group consisting of polyethylene, polypropylene,ethylene copolymers, propylene copolymers, poly(ethylene propylene)copolymers, and combinations thereof.
 7. A method according to claim 1,wherein the rubber comprises a member of the group consisting ofethylene propylene rubber, ethylene propylene diene rubber, andcombinations thereof.
 8. A method according to claim 1, wherein therubber is ethylene propylene diene monomer rubber and the thermoplasticpolyolefinic material is polypropylene.
 9. A method according to claim1, wherein the ground crosslinked rubber is provided by the steps ofcomprising:(a) providing an aqueous slurry of about 10% by weight of 10mesh particles of crosslinked rubber; (b) grinding the slurry in aseries of grinding mills having progressively finer grinding stones. 10.A method according to claim 1, wherein said step (b) is carried outusing a member selected from the group consisting of twin screwextruders, Buss extruders, continuous mill lines, high-speed mixers,low-speed mixers, and combinations thereof.
 11. A method according toclaim 1, wherein said step (b) is carried out by substantially meltingthe thermoplastic polyolefinic material and blending in the rubberparticles.
 12. A method according to claim 1, further comprising a stepof pelletizing the thermoplastic composition to form pellets ofthermoplastic resin.
 13. A method according to claim 12, furthercomprising a step of molding the pellets of thermoplastic resin into anarticle, wherein from about 5% to about 70% by weight of the groundcrosslinked rubber is included in the rubber-blend thermoplasticcomposition.
 14. A method according to claim 12, further comprising astep of extruding the pellets of thermoplastic resin into an article,wherein from about 5% to about 70% by weight of the ground crosslinkedrubber is included in the rubber-blend thermoplastic composition.